Janilabo | Expand()

function Expand(trgt_pos: Integer; s1, s2, str: string): string;
var
  l, start, finish, s1L, s2L: Integer;
begin
  l := Length(str);
  s1L := Length(s1);
  s2L := Length(s2);
  if ((s1L > l) or (s2L > l) or (trgt_pos > l) or (trgt_pos < 1)) then
    Exit;
  finish := PosEx(s2, str, trgt_pos);
  if (finish <= 0) then
    Exit;
  start := LastPosEx(s1, str, trgt_pos);
  if (start < finish) then
    Result := Copy(str, (start + s1L), ((finish - start) - s2L));
end;